Frequently Asked Questions
Metal Inert Gas (MIG) and Metal Active Gas (MAG) welding (known collectively in the USA as GMA welding) offer distinct advantages for welding of cast irons, provided that the special requirements of cast iron welding are borne in mind.
Three modes of metal transfer from the electrode tip in MIG and MAG welding are possible, depending on the heat input. These are spray transfer, globular transfer and short-circuit 'dip transfer', in order of decreasing heat input. Since spray transfer has the highest penetration, it is the least desirable condition for cast iron welding, despite its high deposition rate. Provided that care is taken to avoid incomplete fusion, dip transfer is best suited for welding cast irons since it produces the narrowest HAZ, with the minimum of base metal melting. MIG/MAG welding is used successfully with steel, nickel-based and copper-based consumables, but the choice of consumable depends on the joint performance and appearance requirements.
Flux cored arc welding (FCAW) includes many of the best features of MIG or MAG welding in that it uses a continuously fed wire, and can therefore be easily mechanised, as well as using a flux, which can be used to adjust the weld metal composition and solidification rate. Some cored wire consumables can be used in dip transfer mode, although this will create a lot of spatter and may lead to fusion defects.
The range of consumable types available for FCAW of cast irons is confined to the high nickel, nickel-iron, and nickel-iron-manganese types. The choice of consumables depends on the same factors that govern consumable choice for MMA and MIG/MAG welding.
See also Welding of cast irons - a guide to best practice, from which this FAQ is extracted.